Disable submit form when form invalid Angular + Material

Question

Im building a form using Angular 5.1.1 /Typescript 2.4.2 + Material 5 with sat-popover library

Trying to disable submit button while input is invalid without success. am using the Material Input validation example

validation works and i get an error message, but button is not disabled and form is been submitted with an empty value. i can't figure out how to use the right condition to disable the button while input is invalid. have tried

ng-disabled="!flagForm.valid"

and

ng-disabled="flagForm.$invalid"

when using

[disabled]="!flagForm.valid"

i get 'TypeError: Cannot read property 'valid' of undefined'

none of them seem to work. what am i missing ? here is the full code.

   import { Component, Input, Optional, Host } from '@angular/core';
    import { FormControl, FormGroupDirective, NgForm, Validators} from '@angular/forms';
    import { SatPopover } from '@ncstate/sat-popover';
    import { filter } from 'rxjs/operators/filter';
    import { ErrorStateMatcher} from '@angular/material/core';

    /** Error when invalid control is dirty, touched, or submitted. */
    export class MyErrorStateMatcher implements ErrorStateMatcher {
      isErrorState(control: FormControl | null, form: FormGroupDirective | NgForm | null): boolean {
        const isSubmitted = form && form.submitted;
        return !!(control && control.invalid && (control.dirty || control.touched || isSubmitted));
      }
    } 

    @Component({
      selector: 'inline-edit',
      styleUrls: ['inline-edit.component.scss'], 
      template: `
        <form (ngSubmit)="onSubmit()" name="flagForm" novalidate>
          <div class="mat-subheading-2">Submit Your flag</div>

          <mat-form-field>
            <input matInput maxLength="140" name="flag" [(ngModel)]="flag" [formControl]="flagFormControl"
               [errorStateMatcher]="matcher">
            <mat-hint align="end">{{flag?.length || 0}}/140</mat-hint>
            <mat-error *ngIf="flagFormControl.hasError('required')">
              Flag is <strong>required</strong>
            </mat-error>        
          </mat-form-field>

          <div class="actions">
            <button mat-button type="button" color="primary" (click)="onCancel()" class="btn btn-secondary m-btn m-btn--air m-btn--custom">CANCEL</button>
            <button mat-button type="submit" ng-disabled="!flagForm.valid" color="primary" class="btn btn-accent m-btn m-btn--air m-btn--custom">Submit</button>
          </div>
        </form>
      `
    })
    export class InlineEditComponent {

      flagFormControl = new FormControl('', [
        Validators.required
      ]);

      matcher = new MyErrorStateMatcher();

      /** Overrides the flag and provides a reset value when changes are cancelled. */
      @Input()
      get value(): string { return this._value; }
      set value(x: string) {
        this.flag = this._value = x;
      }
      private _value = '';

      /** Form model for the input. */
      flag = '';

      constructor(@Optional() @Host() public popover: SatPopover) { }

      ngOnInit() {
        // subscribe to cancellations and reset form value
        if (this.popover) {
          this.popover.closed.pipe(filter(val => val == null))
            .subscribe(() => this.flag = this.value || '');
        }
      }

      onSubmit() {
        if (this.popover) {
          this.popover.close(this.flag);
        }
      }

      onCancel() {
        if (this.popover) {
          this.popover.close();
        }
      }
    }

Answer 1

请更正角度禁用的语法

 <button mat-button type="submit" [disabled]="!flagForm.valid" color="primary" class="btn btn-accent m-btn m-btn--air m-btn--custom">Submit</button>

Answer 2

有必要在类中实例化一个表单，像这样

flagForm: FormGroup;

Answer 3

Besides declaring a FormGroup in the class as @tihoroot mentioned, you might want to get an instance of the formControl in the class definition like so:

get flagFormControl() { return this.flagForm.get('flagFormControl'); }

Otherwise Angular cannot find an instance of the required field.

Answer 4

For angular latest you can validate your form in type script using simple below code

Suppose your form looks like this

<form [formGroup]="userForm" novalidate (ngSubmit)="onSubmit()">

you can validate its state like

 if (!this.userForm.valid) {
    return;
  }

Answer 5

Your Form is not defined, to solve this:

In your Component:

flagFormControl: FormGroup = new FormGroup({});

ngOnInit(): void {
// for example
this.flagFormControl= this.formBuilder.group({
      'username': new FormControl('', [Validators.required, Validators.minLength(3)]),
      'email': new FormControl('', [Validators.required, Validators.email]),
      'password': new FormControl('', [Validators.required, Validators.minLength(6)])
    });
}

Or 2nd Option in your Component:

flagFormControl: FormGroup = new FormGroup({
  username: new FormControl('', [Validators.required, Validators.minLength(3)])
... etc
});

and in your Form-html Code:

<form *ngIf="flagFormControl" [formGroup]="flagFormControl" (submit)="createSomething()">
...
<button mat-raised-button color="primary [disabled]="!flagFormControl.valid">Create Something</button>
</form>